DESCRIPTION The research proposed in this application centers around understanding the effects of the endogenous ligands for the mu-opioid receptor, endomorphin I and II on cardiovascular and respiratory regulation. The experimental design will enable the applicant to address the specific aims of this application by examining the peripheral and central contributions of endomorphin-mediated effects in cardiovascular and ventilatory control. The proposed research will further expand on the potential modulatory role of endogenous opioids in the response to hypoxic and hypercapnic stimuli and may contribute to future development of opioid analgesics unconstrained by cardiovascular and respiratory depressant side-effects.